David W. Pascual

Professor

Education

PhD, University of Mississippi Medical Center, Jackson, MS, 1987

MS, University of Mississippi Medical Center, Jackson, MS, 1985

Research

The focus of my laboratory is to understand the basic tenets of mucosal immunology and their application to improve targeted mucosal vaccine delivery. Attenuated Salmonellavectors, adept at delivering vaccines to the Peyer’s patches, elicit T helper (Th) 1 cell (IFN-γ-dependent) immune responses to resolve its infection. However, our studies show we can obtain elevated Th2 cell (IL-4- and IL-13-dependent) immune responses, followed by a delayed onset of Th1 cells to colonization factor antigen I (CFA/I), from human enterotoxigenic Escherichia coli (ETEC). Subsequent studies reveal that proinflammatory cytokine production are abated, suggesting this acts as an anti-inflammatory vaccine. Current studies are evaluating the efficacy of this vaccine against autoimmune diseases such as experimental autoimmune encephalomyelitis (EAE) and collagen-induced arthritis. Our recent findings show this vaccine induces regulatory T (Treg) cells, but the type of regulatory cell induced is disease-dependent: CD25+ Treg (EAE) and CD39+ Tregcells (arthritis). We are currently investigating how Salmonella-CFA/I stimulates the production of these Treg cells, and we are determining the involved dendritic cells that sustain these responses. Recent studies are focused on using the recombinant CFA/I fimbriae, since these were found to be as effective as the live vaccine in reducing arthritis, and on determining the underlying mechanisms for conferring protection against autoimmune insult.

Effective treatments for multiple sclerosis (MS) are problematic due to its unknown etiology. Current work has adapted the rodent EAE model to test whether our tolerogen vaccine delivery platform, the reovirus adhesin, protein sigma 1 (pσ1), can improve mucosal auto-antigen uptake. We have shown a single low-dose of pσ1-based vaccines induces tolerance and prevents or treats autoimmunity when applied mucosally. Amazingly, this new therapeutic can abate MS-like disease within 24 hrs, stimulating an array of regulatory cells to intervene in the central nervous system (CNS). This pσ1-mediated tolerance is, in part, IL-10-dependent via Treg cells. In addition, regulatory elements with the IL-4- and IL-28-producing CD25- CD4+ T cells have also been found. Further work will determine the mechanisms used by pσ1 and will help us to understand the involved dendritic cell subset(s) that stimulates regulatory T cells. Ultimately, these studies will determine the feasibility of using a pσ1-based single-dose delivery system to prevent and/or treat autoimmune diseases.

Members of Category B agents, Brucella species, are highly infectious Gram-negative bacteria that are a global health threat to both humans and livestock. Brucellosis is naturally transmitted via ingestion of unpasteurized dairy products, causing mostly a systemic disease manifesting with flu-like systems, which, despite antibiotic treatment, can cause a recurring sequelae evident as undulant fever and arthritis. Brucellae survival within the host is linked to its ability to resist intracellular recognition, thus, allowing them to sequester in various tissues. Vaccines that can recapitulate aspects of Brucella infection should prove effective to resolve such infections. Yet, to date, there are no effective vaccines for humans and inadequate vaccines for livestock. It is known protection is cell-mediated immunity-dependent and particularly involves TNF-α and IFN-γ. In this regard, we have recently developed live vaccine prototypes that can confer complete protection in some animals with no detectable brucellae. When given orally, these vaccines confer >80% protection against nasal B. melitensis infection, and of these, no brucellae (>4-5 log reduction in tissue colonization) could be detected in host tissues. Given the potency of these vaccine formulations, we are uniquely poised to test the efficacy of these vaccines against parenteral, oral, and pulmonary Brucella challenges.

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